Mitochondrial F(0)F1 ATP synthase - Subunit regions on the F-1 motor shielded by F-0, functional significance, and evidence for an involvement of theunique F-0 subunit F-6

Studies reported here were undertaken to gain greater molecular insight int o the complex structure of mitochondrial ATP synthase (F0F1) and its relati onship to the enzyme's function and motor-related properties. Significantly , these studies, which employed N-terminal sequence, mass spectral, proteol ytic, immunological, and functional analyses, led to the following novel fi ndings. First, at the top of F-1 within F0F1, all six N-terminal regions de rived from alpha + beta subunits are shielded, indicating that one or more F-0 subunits forms a "cap." Second, at the bottom of F-1 within F0F1, the N -terminal region of the single delta subunit and the C-terminal regions of all three alpha subunits are shielded also by F-0. Third, and in contrast, part of the gamma subunit located at the bottom of F-1 is already shielded in F-1, indicating that there is a preferential propensity for interaction with other F-1 subunits, most likely delta and epsilon. Fourth, and consist ent with the first two conclusions above that specific regions at the top a nd bottom of F-1 are shielded by F-0, further proteolytic shaving of alpha and beta subunits at these locations eliminates the capacity of F-1 to coup le a proton gradient to ATP synthesis. Finally, evidence was obtained that the F-0 subunit called "F-6," unique to animal ATP syntheses, is involved i n shielding F-1. The significance of the studies reported here, in relation to current views about ATP synthase structure and function in animal mitoc hondria, is discussed.